Identifying Ions

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Pass the biscuits

Cards (8)

  • How would you carry out a flame test?
    Clean a wire loop in HCl to remove unwanted ions, dip the loop into your sample, place wire with sample in flame, record the colour of the flame.
  • How would you distinguish between aluminium ions and calcium ions?
    Add excess NaOH, Al(OH)3 precipitate reacts to form a colourless solution, Ca(OH)2 precipitate remains unchanged.
  • Describe the test for ammonium ions
    Add dilute NaOH to the sample and warm, ammonia gas is produced which turns damp red litmus paper blue.
  • Describe the test for carbonate ions
    Add dilute acid, pass gaseous product through limewater, CO2 turns limewater cloudy.
  • Describe the test for sulfate ions
    Add a few drops of dilute hydrochloric acid then a few drops of dilute barium chloride solution, white precipitate forms.
  • Why is acid added before testing for sulfate ions, why can’t sulfuric acid be used?
    Carbonate ions react with barium chloride to produce a white precipitate, acid react with CO3(2-) ions to prevent a false positive result. Addition of sulfuric acid would introduce sulfate ions to the sample giving a false positive result.
  • Describe the test for halide ions
    Add dilute nitric acid to react with carbonate ions so no Ag2CO3 forms (white solid). Add silver nitrate, precipitate forms:
    White: AgCl
    Cream: AgBr
    Yellow: Agl
  • Describe the test for carbon dioxide
    Forms a white precipitate for calcium carbonate or turns limewater from colourless to cloudy.